The present invention relates to a circuit arrangement for a timed power supply having an integrated circuit that is connected to first and second supply potential terminals and that comprises a switching mechanism, a control circuit that controls the switching mechanism, and a diode. A coil is also provided, which is connected to the switching mechanism and to a first output terminal. A load is connected between the first and second output terminals and a charge storing device is connected in parallel with the load.
Circuit arrangements for timed switched-mode regulators are taught in a wide variety of configurations. For example, the principal mode of functioning and constructing and operating secondarily timed switched-mode regulators and primarily timed switched-mode regulators is detailed in the book Halbleiterschaltungstechnik (Tietze, U. and Schenk, Ch.; 10.sup.th, ed,1993, Springer:561-576). Besides down converters and up converters, secondarily timed switched-mode regulators also include inverting converters. The advantage of these switched-mode regulators is that a separate transformer is not required, but rather only a storage choke. In the simplest case, secondarily timed switched-mode regulators consist of three components only; namely, a switching transistor, the aforementioned storage choke, and a smoothing capacitor. The switching transistor is constructed as a two-way switch. The two-way switch can be eliminated, however, by including a simple on-off switch in one branch of a down converter and providing a diode in the other branch.
A variety of integrated circuits are known for realizing these types of switched-mode regulators. In the above cited book, on page 567, an integrated module L296 from SGS is described, which internally comprises the series circuit of a bipolar transistor and a freewheeling diode as well as a control circuit for switching the switching transistor on and off.
Down converters, also known as step-down regulators, are used primarily where a low supply voltage must be generated from a high supply voltage with a high degree of effectiveness. In particular, it is noted that a high degree of effectiveness is important above all other considerations in battery-operated devices, for example. Besides achieving a high degree of effectiveness, the heating of electronic components by dissipated power is also of primary importance. This is the case particularly in automotive electronics applications. Despite a high degree of effectiveness, timed power supplies have not previously been applied in automotive electronics due to the lack of electromagnetic compatibility. Instead, linear regulators have been used to generate a regulated supply voltage, though these heat up intensely in operation.
Linear regulators are typically operated in automotive electronics with a nominal current of 400 mA. At a lateral bipolar transistor, the difference between the input voltage and the output voltage drops. The product of the difference between the input and the output voltages and the nominal current is converted into heat loss. The larger the voltage difference between the input and output of the bipolar transistor, the higher the losses. Therefore, due to the sharply rising power loss, it is inappropriate to use a linear regulator in a 42-volt vehicle network. It is therefore desirable to use a switched-mode regulator for load currents of approximately 1 A.
As mentioned above, for reasons of electromagnetic compatibility (EMC), switched-mode regulators have not been used in the automotive field. One possibility for realizing a low EMC radiation is to select a very low timing frequency of the power supply (i.e., in the range from 10 to 40 kHz) and to switch the switching transistor slowly. In this way, the power loss generated by the switching losses can be limited. On the other hand, however, the use of large storage chokes and smoothing capacitors would then be necessary, which are very costly in terms of space and money.
Thus, another possible solution is to use resonance converters, which, with additional resonant circuit elements (coils and capacitors) and diodes, would make possible an approximately sinusoidal voltage and current characteristic. However, resonance converters load the constituent components with higher currents or voltages and also require a significantly higher number of components. Furthermore, the control range with respect to load oscillations and input voltage oscillations is limited.